This is apparently a known issue that Focusrite is working on.
Monday, September 14, 2009
Just a note for any Focusrite Liquid Mix users out there using Snow Leopard - DON'T update to the Mac OS 10.6.1 revision. This is a small revision anyway, apparently to fix some Quicktime problems, but it also doesn't get along with the Liquid Mix. I was able to get it back again by downgrading to 10.6, but it took a lot of messing around.